1. Field of the Invention
The present invention relates to a horizontal rotating hook, having a rotating hook bobbin case holder, for use in a sewing machine. Most horizontal rotating hooks require an opener mechanism that oscillates back and forth to open a path for a needle thread used to form a stitch. In particular, the invention relates to a horizontal rotating hook which does not require an opener that moves the rotating hook bobbin case holder in a direction opposite to the rotation direction of a rotating hook when the loop of a needle thread goes into the rotating hook bobbin case holder.
2. Description of the Background Art
FIGS. 8 to 11 illustrate a conventional horizontal rotating hook device that may be used in a sewing machine. FIG. 8 is a perspective view of the horizontal rotating hook device, FIGS. 9(a) and 9(b) comprise an exploded perspective view showing the horizontal rotating hook device, FIG. 10 is a perspective view showing a throat plate, and FIG. 11 is a top view showing how the horizontal rotating hooks are installed on a twin-needle sewing machine. While there are two types of horizontal rotating hooks for the sewing machine, i.e., a single-piece type integral with a bobbin case and a separate type independent of the bobbin case wherein the bobbin case can be removed from a rotating hook bobbin case holder, the following description deals with the horizontal rotating hook including the single-piece type rotating hook bobbin case holder.
As shown in FIGS. 8, 9(a) and 9(b), the horizontal rotating hook comprises a rotating hook bobbin case holder 1 and a rotating hook 2. Referring to the drawings, the rotating hook bobbin case holder 1 is provided with a rotating hook bobbin case holder position bracket 3, an opener contact 4, a bobbin thread pull-off aperture 5, a bobbin support 6 and a race 7. The rotating hook bobbin case holder position bracket 3 is a projection provided in an external horizontal direction, starting at the cylinder top edge of the rotating hook bobbin case holder 1, to prevent the rotating hook bobbin case holder 1 from rotating. Bracket 3 is fitted into a gap 9 in a throat plate 8 shown in FIG. 10. The gap is formed as a space between two stoppers 9a and 9b provided on the bottom of the throat plate 8, and the width of the gap 9 is larger than the width of the rotating hook bobbin case holder position bracket 3.
The opener contact 4 is a cam colliding with an opener which will be described later. The bobbin thread pull-off aperture 5 is a slit from where the bobbin thread wound around a bobbin 10 (FIG. 11) fitted in the rotating hook bobbin case holder 1 is pulled off to the outside. The aperture 5 is provided in an L shape in the rotating hook bobbin case holder 1. On the external side face of the rotating hook bobbin case holder 1 in this area, a tension spring 11 is secured by screws 12, 13 in such a manner as to cover the bobbin thread pull-off aperture 5. The tension spring 11 shown has a bifurcated or forked front end. Due to the bifurcated shape, the front end fits in a hole 16 provided in the external side face of the rotating hook bobbin case holder 1. The bobbin thread pulled off to the outer periphery of the rotating hook bobbin case holder 1 via the bobbin thread pull-off aperture 5 is lead from the front end portion to a needle hole (which will be described later) along the outer periphery of the rotating hook bobbin case holder 1 and the inside of the tension spring 11. Spring force produced by the tension spring 11 works on the bobbin thread as tension. This tension is adjusted to predetermined tension by tightening and/or loosing the screw 13.
The bobbin support 6, which is a support shaft for loading the bobbin into the rotating hook bobbin case holder 1, is integrated with the rotating hook bobbin case holder 1 at the center of the inner bottom surface of the rotating hook bobbin case holder 1. A bobbin winder stop latch 14, which is provided at the top end portion of the bobbin support 6, is a latch used to prevent the bobbin 10 loaded in the rotating hook bobbin case holder 1 from disengaging. The bobbin stop latch 14 may be moved to work (or set) from a vertical position shown in FIG. 8 to a horizontal position shown in FIG. 9(a)-9(b) by a spring (not shown) in the bobbin support 6. A bobbin winder stop latch groove 15, in which the front end portion of the bobbin winder stop latch 14 fits, is provided at the top edge of the rotating hook bobbin case holder 1. When the bobbin winder stop latch 14 is set into this groove 15, the top height of the bobbin winder stop latch 14 is almost equal to the height of the rotating hook bobbin case holder 1. The race 7 is a projection having a slit provided in the external side face circumference of the rotating hook bobbin case holder 1, and its action will be described later.
The rotating hook 2 is provided with a hook point 20, a race groove 21 and a rotating hook shaft 22. The hook point 20 is a thread loop capturing catch which captures a loop formed by the needle thread and goes along the outer periphery of the rotating hook bobbin case holder 1. Stitches are formed by means of the needle and bobbin threads. The race groove 21 is a groove where the race 7 of the rotating hook bobbin case holder 1 fits and which comprises the rotating hook 2 above which top surface a rotating hook section 23 is fixed by screws 23a, 23b. A back plate 24 is secured to the external bottom surface of the rotating hook 2 by screws 24a, 24b.
The rotating hook shaft 22 functions to transmit rotation from a lower shaft (not shown) of the sewing machine to the rotating hook and simultaneously actuate the opener which will be described later. For this purpose, an eccentric shaft 25 is formed integrally at the top of the rotating hook shaft 22. A through hole 26 is provided in the rotating hook shaft 22 to supply lubricant to the race portion via an oil string fitted therein.
The horizontal rotating hook device consists of the horizontal rotating hook and an opener mechanism. As shown in FIGS. 9(a)-9(b) and 11, the opener mechanism comprises an opener 30, an opener support 31 and a connecting arm 32. The connecting arm 32 is an arm for jointly operating the eccentric shaft 25 of the rotating hook shaft 22 and the opener support 31. The arm 32 has two rings, one of the two rings is fitted with the eccentric shaft 25 and the other is secured rotatably to the opener support 31 by a stepped screw 33 and a nut 34. The opener 30 is installed on the arm portion of the opener support 31 by a screw 35, and an opener support shaft 36 is fitted into a ring which serves as the supporting point of the opener support 31. This shaft 36 is screwed to a hook saddle (not shown) secured on a sewing machine bed.
The horizontal rotating hook device arranged as described above is installed onto the sewing machine bed (not shown) as shown in FIG. 11. As seen from FIG. 11, the opener 30 collides with the opener contact 4 of the rotating hook bobbin case holder 1 in a positional relationship as shown. A feed dog 40 is located in the slot of the throat plate 8. This feed dog 40, which is fixed to a feed bar (not shown) of a sewing machine feed mechanism, makes an elliptical feed motion in synchronization with a needle motion. When this motion works on a fabric inserted between a presser mechanism and the feed dog, the fabric is fed. A needle hole 41 is provided in the center of the feed dog 40.
The operation of the horizontal rotating hook and opener mechanism will now be described. Referring to FIG. 11, when the sewing machine is rotatively driven, the rotating hook 2 fully rotates in the direction of arrow A (clockwise) and the opener 30 oscillates back and forth in the directions of arrows B and C at an angle determined by pitch lengths between the screws 33, 35 and opener support shaft 36 and by the eccentricity of the eccentric shaft 25, with the opener support shaft 36 acting as a supporting point. This oscillatory motion of the opener 30 allows the needle thread coming from the needle to easily pass the rotating hook bobbin case holder position bracket 3 and fully go along the outer periphery of the rotating hook bobbin case holder 1.
How the needle thread goes along the rotating hook bobbin case holder will now be described in detail with reference to FIGS. 12 to 14. FIG. 12 is a top view which illustrates how the needle thread is pulled off by the horizontal rotating hook device, FIG. 13 is a similar top view for the bobbin thread, and FIG. 14 is a sectional view taken along the plane E--E of FIG. 12. In FIG. 12, the numeral 50 indicates the needle thread. How it goes along the outer periphery of the rotating hook bobbin case holder 1 also is illustrated. Namely, as the hook point 20 (FIG. 9(a) of the rotating hook 2 having captured the loop of the needle thread turns in the direction of arrow A, the loop of the needle thread 50 advancing along the outer periphery of the rotating hook bobbin case holder 1 moves sequentially from position 50a to position 50b. Position 50a indicates an instant when the needle thread 50 passing through the needle hole 41 has disengaged from the stopper 9a of the throat plate 8 and is just entering the gap 9. At this point, the opener 30 is displaced at its maximum in the direction of C. Hence, the rotating hook bobbin case holder position bracket 3 of the rotating hook bobbin case holder 1 is forced to move to position 3a indicated by a broken line, where space S1 is formed between the rotating hook bobbin case holder position bracket 3 and the stopper 9a. For convenience of explanation, this space S1 is herein referred to as a first space.
In the meantime, the rotating hook bobbin case holder 1 is generally given rotating force in the direction of arrow A by frictional torque between itself and the rotating hook 2. For this reason, the rotating hook bobbin case holder position bracket 3 is pressed against the stopper 9a. In addition to this pressure force, the pull-off tension of the bobbin thread is further applied. In FIG. 13, which shows the path of the bobbin thread 51 pulled off from the bobbin 10, the position of the bobbin thread pull-off aperture 5 is within the range of two right angles in the counterclockwise rotating direction of the rotating hook 2 with respect to a segment connecting the center of the bobbin support 6 and the rotating hook bobbin case holder position bracket 3. Hence, the pull-off tension of the bobbin thread 51 works in a direction in which the rotating hook bobbin case holder 1 is rotated in the direction of arrow A. Generally, the set tension of 0.3 to 1N is applied beforehand to the bobbin thread 51 by the tension spring 11. This tension increases if the bobbin thread is pulled off at high speed.
Accordingly, the opener 30 rotates and displaces the rotating hook bobbin case holder 1 in a direction opposite to arrow A against the pressure force based on fractional torque and the pull-off tension of the bobbin thread. Consequently, as shown in FIG. 14, the needle thread 50 on the needle side shifts from continuous-line position 50c to broken-line position 50d. Namely, the needle thread passes the first space.
Thereafter, when the needle thread 50 reaches position 50b in FIG. 12 in the progress of rotation, the opener 30 is displaced at its maximum in the direction of arrow B. Along with this, space S2 is produced between the rotating hook bobbin case holder position bracket 3 and the stopper 9b of the throat plate 8, whereby the loop of the needle thread 50 passes the rotating hook bobbin case holder section easily. For convenience of explanation, this space S2 is referred to as a second space. When the needle thread 50 finishes rotating along the rotating hook bobbin case holder 1, the needle thread 50 is tangled with the bobbin thread, forming a stitch.
In the conventional horizontal rotating hook for use in the sewing machine arranged as described above, the opener mechanism was indispensable for the loop of the needle thread to go through into the rotating hook bobbin case holder and form stitches along with the bobbin thread. However, the opener impinged on the opener contact of the rotating hook bobbin case holder and further the rotating hook bobbin case holder position bracket impinged on the stopper of the throat plate, generating significant noise. When the sewing machine was driven at high speed, e.g. 4000 r/min., the noise level sometimes exceeded 90 dB(A), hindering stitching worker operability considerably. Also, the impingement of the rotating hook bobbin case holder position bracket on the stopper of the throat plate caused the rotating hook bobbin case holder position bracket to result in fatigue failure.